Introduction
Vegetables and fruit are extremely important in human nutrition as sources of nutrients and non-nutritive food constituents as well as for the reduction in disease risks. While their importance as sources of nutrients and non-nutritive food constituents is generally accepted, there are still uncertainties regarding their relevance for the prevention of diseases. For this reason, it has to be determined first, for which diseases studies have detected an association between the consumption of vegetables and fruit and the risk of disease, and subsequently, how this association has to be judged. This information provides an important basis to judge the preventive potential of a diet rich in vegetables and fruit. For example, this would allow to estimate the changes regarding the incidence of certain diseases that have to be expected if, for example, the “5 a day” recommendation on the consumption of about 650 g vegetables and fruit per day would be implemented by the majority of subjects in Germany.
Therefore, a working group within the German Nutrition Society (DGE) was established in 2006 with the aim to evaluate the evidence on the role of vegetables and fruit regarding the prevention of certain chronic diseases. The available data were recorded by comprehensive literature search, and the respective strength of the evidence was determined by criteria defined in advance. This evaluation of the evidence was published in 2007 in German as a DGE-statement [1].
As further studies on the association between the consumption of vegetables and fruit and the risk of disease have been published since 2007, it was necessary to update the statement. Therefore, the available data on the diseases selected in 2007 once again were comprehensively recorded with focus on prospective epidemiologic observational and intervention studies, and based upon these study data, the evidence regarding a preventive effect was judged.
Methods
The review is based upon the comprehensive analysis of the epidemiological studies available in the literature on vegetables and fruit. The authors agreed at the beginning of the study to cover the same list of diseases that were included into the DGE-statement from 2007 [1] since no other disease group than the previously selected appeared to be newly associated with consumption of vegetables and fruit. For each disease under consideration, a literature search in the NCBI PubMed database was done that included the literature until December 2010. The search strategy comprised the keywords “fruit” and “vegetables” and the various disease outcomes (Table 1). The type of studies that are searched for differed according to endpoint. Based on the experience from the DGE-statement from 2007 [1], for some endpoints such as type 2 diabetes, hypertension, coronary heart disease, stroke, and cancer, the search had been restricted to intervention and cohort studies. For other endpoints, all types of epidemiological studies had been looked at in the database. In addition to the studies identified in the newly conducted literature search, the references in relevant publications were reviewed in order to have identified all of the studies. Also, the literature research in conjunction with the DGE-statement from 2007 [1] was taken into account. Furthermore, studies that have been published until April 2011 were included in the review if they contain new information relevant for the judgement of the evidence.
Table 1
Introduction
Vegetables and fruit are extremely important in human nutrition as sources of nutrients and non-nutritive food constituents as well as for the reduction in disease risks. While their importance as sources of nutrients and non-nutritive food constituents is generally accepted, there are still uncertainties regarding their relevance for the prevention of diseases. For this reason, it has to be determined first, for which diseases studies have detected an association between the consumption of vegetables and fruit and the risk of disease, and subsequently, how this association has to be judged. This information provides an important basis to judge the preventive potential of a diet rich in vegetables and fruit. For example, this would allow to estimate the changes regarding the incidence of certain diseases that have to be expected if, for example, the “5 a day” recommendation on the consumption of about 650 g vegetables and fruit per day would be implemented by the majority of subjects in Germany.
Therefore, a working group within the German Nutrition Society (DGE) was established in 2006 with the aim to evaluate the evidence on the role of vegetables and fruit regarding the prevention of certain chronic diseases. The available data were recorded by comprehensive literature search, and the respective strength of the evidence was determined by criteria defined in advance. This evaluation of the evidence was published in 2007 in German as a DGE-statement [1].
As further studies on the association between the consumption of vegetables and fruit and the risk of disease have been published since 2007, it was necessary to update the statement. Therefore, the available data on the diseases selected in 2007 once again were comprehensively recorded with focus on prospective epidemiologic observational and intervention studies, and based upon these study data, the evidence regarding a preventive effect was judged.
Methods
The review is based upon the comprehensive analysis of the epidemiological studies available in the literature on vegetables and fruit. The authors agreed at the beginning of the study to cover the same list of diseases that were included into the DGE-statement from 2007 [1] since no other disease group than the previously selected appeared to be newly associated with consumption of vegetables and fruit. For each disease under consideration, a literature search in the NCBI PubMed database was done that included the literature until December 2010. The search strategy comprised the keywords “fruit” and “vegetables” and the various disease outcomes (Table 1). The type of studies that are searched for differed according to endpoint. Based on the experience from the DGE-statement from 2007 [1], for some endpoints such as type 2 diabetes, hypertension, coronary heart disease, stroke, and cancer, the search had been restricted to intervention and cohort studies. For other endpoints, all types of epidemiological studies had been looked at in the database. In addition to the studies identified in the newly conducted literature search, the references in relevant publications were reviewed in order to have identified all of the studies. Also, the literature research in conjunction with the DGE-statement from 2007 [1] was taken into account. Furthermore, studies that have been published until April 2011 were included in the review if they contain new information relevant for the judgement of the evidence.
Table 1
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